Laying out a square area for a garden bed or another project can be achieved by applying the 3-4-5 rule. The objective of this method is to have all four sides of the square of equal length and all four corners 90-degree right triangles. The sides of the square can be any length, but the legs measured for the right triangle must be multiples of 3, 4 and 5. It’s not as complex as it sounds. For instance, a garden bed can be 10 feet square, but the triangle to square it is either three-by-four-by-five-feet or six-by-eight-by-ten-feet. Larger triangles yield more accurate results.
Choose the site where you want to lay out a square area. Hammer a stake into the ground about where each of the four corners will be on the square. Be sure to measure between stakes so they are all equal distance apart. For this example, measure 10 feet from the first stake to the second and on around the square with all being 10 feet apart.
Tie a mason string around the top of one of the the stakes, and call this "stake B." Run the string down one side of the square to another stake: stake C. Tie it off near the top. Run it from stake B down the other side of the square to the other stake -- stake A -- and tie it off to the top.
Measure 6 feet from stake B toward stake C. Mark this point on the string using a permanent marker.
Measure 8 feet from stake B to stake A. Mark this point on the string using a permanent marker.
Measure the diagonal between the two points you marked on the string. The tape measure will form a right triangle with the strings. It should be precisely 10 feet on the tape measure from string to string. Pull up either stake A or B, not both, and move it inward or outward so the length of the diagonal is 10 feet. Having a helper move the stake while you watch the tape makes this task easier. You may also need a third person to hold the other end of the tape measure. When the string is at 10 feet, re-hammer the stake into the ground. Re-check the measurement after the stake is set.
Move to stake C and repeat the process for forming a right triangle at each of the remaining three stakes. When you have formed a right triangle at each corner you’ll have a square bed.